1. Field of the Invention
The present invention pertains to cataract surgery and, more particularly, to the prevention of clouding of the posterior capsule after extracapsular cataract extraction.
2. Discussion of the Prior Art
Clouding of the posterior capsule after extracapsular cataract extraction, with or without the implant of an intraocular lens, has been a principal, later occurring, complication of such extracapsular cataract surgery. During cataract surgery, it is preferable to extract the natural lens while leaving the posterior portion of the lens capsule intact in front of the vitreous cavity of the eye to provide a barrier to prevent anterior movement or loss of the vitreous which fills the cavity and to also provide a support for an intraocular lens implanted in the posterior chamber. If the natural lens is removed intact with the capsule, referred to as intracapsular cataract extraction, the vitreous can move through the pupil causing vitreous loss and increasing the chances of complications, such as glaucoma, corneal opacity, displacement of an intraocular lens, retinal hemorrhage, holes, breaks and detachment, and cystoid macula edema.
In many cases after extracapsular cataract extraction, with or without the implant of an intraocular lens, the posterior capsule becomes opacified or clouded due to migration of proliferating undifferentiated epithelial cells into the optical zone which, clustered, form Elschnig's pearls. Along with Elschnig's pearls, visual acuity is also reduced by invading fibroblasts through metaplasia developing into myoepithelial fibers, lens fibers, collagen, fibrosis and Sommering rings. This opacification or clouding of the posterior capsule, referred to as secondary cataract, occurs in a large percentage of extracapsular cataract extractions and is a primary cause of post operative complications.
One procedure to remove secondary cataracts is discission using a needle or scissors to punch or cut a hole in the posterior capsule. Another procedure includes the use of a YAG laser focused through the pupil to open the posterior capsule. Such procedures, referred to as posterior capsulotomy, remove the opacification to improve sight; however, they also create the adverse effects discussed above with respect to intracapsular cataract extraction due to the removal of the barrier to vitreous movement.
Other attempts to prevent clouding of the posterior capsule include constructing intraocular lenses to produce barriers to movement of the undifferentiated epithelial cells from the equator of the posterior capsule toward the optical zone; however, such intraocular lenses have been difficult to implant in the posterior capsule and have not created effective barriers to prevent clouding.
Still another attempt to prevent proliferation of lens epithelial cells after extracapsular cataract extraction is shown in U.S. Pat. No. 4,432,751, to Emery et al, which instills monoclonal antibodies specific to lens epithelial cells into the anterior chamber to cause lysis or other damage to the lens epithelial cells and prevent the cells from multiplying and covering the posterior lens capsule.
Accordingly, there is a great need for a manner in which to prevent opacification of the posterior capsule, particularly in view of the great number of cataract surgeries performed each year and the substantial likelihood of most individuals having cataract surgery due to the natural forming of cataracts in the natural lens with aging. As noted above, the preferable procedure for cataract surgery is extracapsular cataract extraction; and, thus, much effort has been directed toward overcoming the late capsule clouding complication associated with such cataract surgery.